Shadow-mask having rectangular apertures

ABSTRACT

The electron gun unit housed in a neck portion of a tube envelope consists of three electron guns corresponding to red, green and blue. The electron gun corresponding to blue is smaller in diameter than the remaining electron guns, and the axes of said electron guns are arranged to form an isosceles triangle in such a manner that the electron gun having a small diameter has its axis on the apex of the isosceles triangle. Fluorescent dots upon which electron beams emitted from said electron guns impinge are substantially in the form of thin rectangles or ellipses which extend substantially at right angles to the beam scanning direction. Adjacent to said fluorescent dots is disposed a shadow-mask having a plurality of rectangularly shaped beam passing holes.

United States Patent Tsuneta et al.

[151 3,663,854 1 May 16, 1972 [22] Filed:

[54] SHADOW-MASK HAVING RECTANGULAR APERTURES Tokyo Shibaura Eleeric Co., Ltd., Kawasaki-shi, Japan Feb. 12, 1970 [21] Appl. No.: 10,978

[73] Assignee:

[30] Foreign Application Priority Data Feb. 17, 1969 Japan ....44/1 1084 [52] US. Cl ..3l3/85 S, 313/92 B [51] int. Cl ..H0lj 29/06, HOlj 31/20, HOlj 29/30 [58] Field otSearch ..3l5/l3 CG,21 C;3l3/85 S, 313/92 B [56] References Cited UNITED STATES PATENTS 2,764,628 9/1956 Bambara ......3l3/85 S X 2,850,658 9/1958 Allwine ..3l3/70 C X 2,922,073 l/ 1960 Oestreicher ..3l3/92 B X 3,393,336 7/1968 De France et a1 ..3 1 3/70 C FOREIGN PATENTS OR APPLICATIONS 393,417 10/1965 Switzerland ..3l3/85 S 807,129 l/l959 Great Britain ..3l3/85 5 Primary Examiner-Robert Segal AttorneyFlynn & Frishauf [57] ABSTRACT The electron gun unit housed in a neck portion of a tube envelope consists of three electron guns corresponding to red, green and blue. The electron gun corresponding to blue is smaller in diameter than the remaining electron guns, and the axes of said electron guns are arranged to form an isosceles triangle in such a manner that the electron gun having a small diameter has its axis on the apex of the isosceles triangle. Fluorescent dots upon which electron beams emitted from said electron guns impinge are substantially in the form of thin rectangles or ellipses which extend substantially at right angles to the beam scanning direction. Adjacent to said fluorescent dots is disposed a shadow-mask having a plurality of rectangularly shaped beam passing holes.

4 Claims, 5 Drawing Figures atented May 16, 1972 ,2 Sheets-Sheet 1 FIG.1

FIG.2

Q b L 1 SHADOW-MASK HAVING RECTANGULAR APERTURES This invention relates to cathode-ray tubes and more particularly to an improved color cathode-ray tube of the shadow-mask type.

A known color cathode-ray tube of this nature disadvantageously producesa dark image picture due to the fact that electron beams emitted from electron guns are mostly impinged upon a shadow-mask and thereby consumed when they pass through beam passing holes formed in the mask so that the beam effectively impinged on a fluorescent surface is of less intensity.

More particularly, the beam passing holes in a prior art tube are circular and electron beams emitted from three electron guns corresponding to red, green and blue are passed through the beam passing holes intersectingly at different angles. The fluorescent surface has three circular'fluorescent dots of red, green and blue for a single beam passing hole at places thereof to be impinged. Beam deflection errors, however, are caused at the edge portions on the fluorescent surface, while at the central portion thereof the electron guns are subjected to physical deformation mainly due to heat, thus causing a shift between places to be impinged by the beams and the fluorescent dots. In an extraordinary case, beams are not directed to fluorescent dots to be normally impinged but are impinged on adjacent dots of a different color, thus causing non-registration of colors. In order to eliminate these drawbacks, it has been a common practice to form the area of each dot greater than that actually impinged. Thus, the diameter of the beam passing holes has been necessarily restricted under a certain value, which decreases the amount of beams effectively impinged on the fluorescent surface. For the reason described hereinbefore, a beam spot should be produced on the central portion of the fluorescent dot due to the impingement of beam. For the purpose of description, a portion of the dot that surrounds the beam spot and is not impinged will hereunder be termed guard ring.

Further in a prior art device of the three electron gun type, all-the three electron guns have the same outside diameter and are arranged such that their axes define the apices of a normal (equilateral) triangle. When the amount of beam deflection power is to be decreased, the outside diameter of each electron gun will have to be uniformly reduced thereby to narrow the neck portion of an envelope around which a beam deflec tion device is to be mounted. However, this reduction in the outside diameter of the electron guns will necessitate a reduction in the outside diameter of electron lenses within the electron guns. As a result, there tends to be produced a spherical aberration to the beams and the quality of picture images is unavoidably lowered.

Accordingly, the object of this invention is to provide a shadow-mask type color cathode-ray tube in which the transmittivity of electron beams of a shadow-mask can be increased without damaging the color reproduction property, to provide a light image and in which the outside diameter of a neck portion thereof can be minimized without causing spherical aberration, thereby decreasing the beam deflection power.

SUMMARY OF THE INVENTION According to this invention, the above object can be attained by the provisions of fluorescent dots shaped substantially in the form of a long, non-circle, namely, a thin or long rectangle or ellipse and which extend in a direction substantially perpendicular to a beam scanning direction, a shadowmask provided with substantially rectangular beam passing holes disposed adjacent to said dots, and an electron gun unit including three electron guns corresponding to red, green and blue wherein said electron gun corresponding to blue is smaller in outside diameter than the rest. The electron guns are arranged in the form of an isosceles triangle with the blue election gun forming the apex of the triangle.

This invention can be more fully understood from the following detailed description when taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of the color cathoderay tube embodying this invention;

FIG. 2 is an enlarged plan view showing a part of a shadow mask shown in FIG. 1;

FIG. 3 is a similar view showing a part of a fluorescent layer shown in FIG. 1;

FIG. 4 is a schematic view showing the arrangement at tip ends of electron guns of a three-electron gun unit shown in FIG. 1; and

FIG. 5 shows the relative positions of various elements of the cathode-ray tube of this invention.

The structure of the color cathode-ray tube according to this invention will be briefly described with reference to FIG. 1. The cathode-ray tube comprises a glass bulb 1 and a shadow-mask 7. The glass bulb 1 comprises a neck portion 2 having therein three electron guns 3a, 3b and 3C corresponding to red, green and blue, a funnel portion 4 connected to said neck portion 2 and extending therefrom in the form of a funnel, and a face plate 5 connected to the open edge of said funnel portion 4 and provided with a fluorescent layer 6 formed of red, green and blue fluorescent dots. The shadowmask 7 is positioned adjacent to the fluorescent layer 6 by means of a supporting frame 11 supported by a supporting member (not shown) and includes a plurality of beam passing holes 8 of such a shape as will be described later. Although not shown, a beam deflection device is provided on the outer circumference of the neck portion 2.

In order to sufficiently increase the transmittivity at the shadow-mask 7 of electron beams to be emitted from the electron guns 3a, 3b and 3c, and to reduce the diameter of the neck portion 2 thereby to decrease the deflection power to be used, the following experiments and studies have been carried out. As shown in FIG. 4, each electrode of the electron guns 3a and'3b corresponding to red and green has been varied in diameter from the electrode of the electron gun 3c for blue. More particularly, the electrode of the electron gun 30 has been formed to have a diameter smaller than that of each electrode of the remaining electron guns. Further, the electron guns have been arranged in such a manner that their axes define a non-equilateral triangle, namely an isosceles triangle having its apex corresponding to the axis of the electrode of the electron gun 3c for blue. It has been found that, with the arrangement above described, the electron guns may be disposed in the neck portion 2 of a diameter sufiiciently small not to substantially increase spherical aberration and to decrease the deflection power. The electron gun 3b in charge of green gives great influence on the resolution of a color picture, and red tends to become conspicuous when the electron beam causes an aberration. The reason for forming the electrode of the electron gun 3c (blue) to have a smaller diameter than those of the other electron guns is due to the fact that its influences on resolution and aberration are relatively inconspicuous as compared with those for red and green.

With the above described isosceles triangular arrangement and the shadow-mask 7 having a plurality of beam passing holes which are not circular as in the prior art, but are substantially long rectangles as shown in FIG. 2, extending in a direction substantially perpendicular to the direction of scanning the electron beam, as shown in FIG. 2, the distance between a screen (the fluorescent layer 6) and the shadowmask and the position of a light source, namely, the position of the beam at a deflection plane (See FIG. 5.), at the time of depositing and heating fluorescent dots by use of an exposure platform (not shown) commonly employed in the manufacture of cathode-ray tubes can be established on the basis of a horizontal component Sgx Sg-CosH, with respect to the screen, viz. a component acting in the direction of beam scanning or the direction of x, without using the distance Sg between the image screen and the axes of the electron guns for red Rg and green Gg. In FIG. 2,

a is the horizontal pitch of the beam passing holes 8 in the shadow-mask,

b is the vertical pitch thereof,

d is the horizontal length thereof, and

e is the vertical length thereof.

FIG. 3 illustrates fluorescent dots R, 100 and 108 where:

f is the spacing with respect to the horizontal direction (beam scanning direction) between the two given fluorescent dots,

a1 is the pitch of the dots for the same color with respect to the horizontal direction, and

d1 is the horizontal length of the dots.

As will be apparent from FIG. 3, the relationship d1 f holds. The dots 6 and the holes 8 may be thin ellipses other than rectangles. The distance mentioned can be represented in terms of the distance Sx of the deflected position of the electron beams within the deflection plane from the axis of the electron gun unit, by denoting the distance between the tip end of the electron gun and the fluorescent screen 6 as Lsg, the distance in the line scanning direction between the tip portion of the electron gun and the axis of the electron gun unit as Sgx, the distance between the beam deflection position of the deflection device and the screen 6 as L, the distance between the shadow-mask and the screen 6 as q, the pitch of the holes 8 in the shadow-mask as a, and further by denoting, as described above, the horizontal spacing between the fluorescent dots shown in FIG. 3, for example, between the dots 10B and 10R as f.

From FIG. 5, the spacing q between the shadow-mask 7 and the screen 6 and said distance Sx can be represented by al=3f= aL/(L-q) f/Sx q/(L-q) hence,

q aL/3Sx (I) Since Sgx.(Lsgq)=Sx:(L-q), the distance Sx can be easily determined by:

Sx Sgx:(L q)/ (Lsg q) (2) from which the position of the axes Rg and Gg of the electron guns 3a and 3b can be determined. As shown in FIG. 4, the axis of the electron gun electrode Bg in charge of blue is generally located on the Y-axis extending in the direction substantially perpendicular to said direction of beam scanning and has a diameter smaller than those of the other electrodes Rg and Gg, so that the electrode Bg with its axis located on the Y-axis may be disposed in a position closer to the other two electrodes in such a manner that the axes of the respective electrodes take the apices of an isosceles triangle, with the result that the overall outside diameter of the electron gun unit can be reduced. For example, the electron gun 30 (blue) may be about 7 mm in outside diameter and each of the electron guns 3a and 3b may have an outside diameter of about 10 mm, thereby reducing the overall diameter of the unit to attain the aforesaid purposes. The position of shadow-mask and the fluorescent screen can be determined from the equations (1 and (2) above on the basis of the above arrangement of the electron guns.

According to this invention, even if there occurs a small amount of mislanding of the electron beam with respect to the longitudinal direction of the fluorescent dots 10R, 106 and 10B, it only permits the fluorescent dots in the same color to be radiated, and the fear of producing color shifting can be eliminated. With respect to said guard ring, only a lateral or horizontal component of the dots may be taken into consideration. The width GR of the guard ring can be obtained from GR (d1 d )/2 where d is the lateral or horizontal length of a beam spot and d1 f 01/3. Between d and the lateral length d of the holes in the shadow-mask exists the experimental relationship d 1.15d. Thus, the width of the guard ring perpendicular to the direction of scanning be ignored, so that the size of the holes 8 in the shadow-mask 7 may accordingly be increased to provide an improved beam transmittivity, which may be obtained, from FIG. 2, by:

T= d x e/a x b (3) The invention will now be described with respect to one example thereof. A cathode-ray tube was prepared in the manner shown in FIG. 5 by respectively selecting the distance Lsg between the tip ends of electron guns and a fluorescent screen to 264 mm, the distance L between a deflection plane to the fluorescent screen to 194 mm, the pitch of holes in a shadow-mask with respect to a horizontal direction to 0.60 mm, the distance Sg between the central axis of the electron gun unit and the electrode axes (red and blue) at the tip ends thereof to 5.78 mm, the distance Sgb between the central axis of the electron gun unit and the axis of the electrodes (blue) to 6.79 mm, and the angle 0 of the axis of each of the electron guns (red and green) with respect to the X-axis to 16". As a result, q 9.63 mm, 8): 4.03 mm, a1 0.63 mm and d1 0.21 mm. Assuming that GR (only in respect of a horizontal direction) is 0.05 mm, then d= 0.10 mm, e =3.00 mm and b =3. 10 mm in FIG. 2. An excellent transmittivity was obtained since T= 15.9 percent from the equation (3).

The various characteristics of the shadow-mask type color cathode-ray tube according to this invention, a conventional shadow-mask type cathode-ray tube, and a tube prepared for the purpose of the comparison with this invention and comprising electron guns of isosceles triangular arrangement and a known shadow-mask are shown in the table below.

glio ray tube with electron guns of isosceles triangular arrangement and shadow-mask having circular holes (comparison).

3 This invention.

4 Horizontal direction.

It will be seen from the table that the tube of this inveiition displays various improvements. In particular, it has been found that from the results shown the luminescence of the tube can be greatly improved by 20 to 43 percent as compared with those of the tubes for comparison. Further, since the electron guns are arranged in the form of a nonequilateral triangle, in particular, an isosceles triangle, the overall diameter of the electron gun unit can be reduced when compared with that in a known device, whereby the amount of deflection voltage can be decreased.

The axis of the electron gun (blue) has been described to be perpendicular to the direction of beam scanning. I-Iowever, similar results will be obtained by arranging said axis in such a position as that of said red or green electron gun in the manner already discussed.

What we claim is:

1. A shadow-mask type color cathode ray tube comprising:

an evacuated envelope;

a multi-color image screen including a plurality of interspersed groups of elemental fluorescent dots including blue;

electron gun means including a plurality of electron guns for projecting a corresponding plurality of electron beam components towards said image screen, said electron gun corresponding to the blue fluorescent dots having an outside diameter smaller than those of the other electron guns, and said electron guns being arranged in an isosceles triangle having its apex corresponding to said electron gun for blue; and

a shadow-mask having a plurality of substantially rectangular shaped apertures therein, said shadow-mask being disposed between said screen and said electron gun means for selectively directing said electron beam components onto said fluorescent dots;

the distance Sx between a position at which each of said beam components is deflected and the axis of the electron gun unit as measured in the direction of scanning, and the distance q between the shadow-mask and the fluorescent surface being defined by where a is the pitch of the beam passing apertures of said shadow-mask in the direction of scanning, L is the distance between the deflection position and the fluorescent surface, Sgx is the distance in the direction of scanning between the tip portion of the electron gun and the axis of the electron gun unit, and Lvg is the distance between the tip end of each electron gunand the fluorescent surface.

2. A shadow-mask type color cathode-ray tube according to claim 1 wherein said fluorescent dots in each group are red, 

1. A shadow-mask type color cathode ray tube comprising: an evacuated envelope; a multi-color image screen including a plurality of interspersed groups of elemental fluorescent dots including blue; electron gun means including a plurality of electron guns for projecting a corresponding plurality of electron beam components towards said image screen, said electron gun corresponding to the blue fluorescent dots having an outside diameter smaller than those of the other electron guns, and said electron guns being arranged in an isosceles triangle having its apex corresponding to said electron gun for blue; and a shadow-mask having a plurality of substantially rectangular shaped apertures therein, said shadow-mask being disposed between said screen and said electron gun means for selectively directing said electron beam components onto said fluorescent dots; the distance Sx between a position at which each of said beam components is deflected and the axis of the electron gun unit as measured in the direction of scanning, and the distance q between the shadow-mask and the fluorescent surface being defined by q aL/3Sx Sx Sgx (L-q)/(Lsg-q) where a is the pitch of the beam passing apertures of said shadow-mask in the direction of scanning, L is the distance between the deflection position and the fluorescent surface, Sgx is the distance in the direction of scanning between the tip portion of the electron gun and the axis of the electron gun unit, and Lsg is the distance between the tip end of each electron gun and the fluorescent surface.
 2. A shadow-mask type color cathode-ray tube according to claim 1 wherein said fluorescent dots in each group are red, green and blue, and said electron gun means includes electron guns for projecting red, green and blue electron beam components.
 3. A shadow-mask type color cathode-ray tube according to claim 1 wherein said fluorescent dots are rectangular dots.
 4. A shadow-mask type color cathode-ray tube according to claim 1 wherein the ratio between the electron gun corresponding to blue and the other electron guns is 7:10 in outside diameter. 